1. Field of the Invention
This invention relates to a storage system having a plurality of physical storage devices (for example, hard disk drives), and in particular to technology to provide a power supply to a plurality of storage devices.
2. Description of the Related Art
Storage systems of which RAID systems are representative comprise numerous storage devices, such as for example hard disk drives (hereafter abbreviated “HDD”). In Japanese Patent Laid-open 4-78062, a RAID system configured to supply power to a plurality of HDDs from the same power supply circuit is described.
In general, each of the HDDs installed in such a storage system is assembled as a single unit (hereafter called a “HDD unit”) in which the group of components necessary to function as an HDD (for example, the magnetic disks, read/write heads, power transmission mechanisms and other mechanical components, the motors and other electromechanical components needed to drive the former, and the driver circuits for the electromechanical components, logic circuits for data processing, microprocessors, and other electrical circuit components) are indivisibly integrated and fixed in a single casing. An HDD unit has connectors for connection to data communication circuits within the storage system and to power supply circuits. The physical specifications of the connectors are characteristic of the specifications of the interface for data transfer adopted by the HDD; typically, an HDD unit has a prescribed plurality of data transfer terminals and a prescribed plurality of power supply terminals. There are various electrical circuit components within an HDD unit, and different types of circuit components require power supplies at different voltage levels. For example, logic circuits for data communication and control require a 5 V_DC power supply, whereas motors, heads, and other actuators require a 12 V_DC power supply. A plurality of power supply terminals among the connectors are allocated to such power supplies with different voltage levels.
Efforts are made each year to expand the capacity of this type of storage system, and the number of HDD units installed increases steadily. In addition, higher reliability, more compact size, and lower prices are also sought. Further, as magnetic disks move toward higher densities, faster data transfer rates and higher revolution rates, there is a trend toward increased power consumption within HDD units. On the other hand, there is also a trend towards diversification of the specifications of power supplied to HDD units within a storage system. Also, there is a trend toward adoption of interface specifications for data transfer to HDD units enabling faster operation and lower prices, such as for example the Small Computer System interface (hereafter abbreviated to “SCSI”), Fiber Channel Interface (hereafter “FC”), and Serial ATA (hereafter “SATA”).
Given the above circumstances, there are the following problems and demands.
(1) The number of power supply terminals of the connector of an HDD unit is fixed at a certain number by the specifications of the interface for data transfer, and there is a constant upper limit to the current which can flow to each power supply terminal. For example, FC specifications stipulate that a connector has four power supply terminals, and that the upper limit to current which can flow through one power supply terminal is 1 A. Normally, two power supply terminals are allocated for 12 V_DC, and two power supply terminals for 5 V_DC. Hence only current up to 2 A can be supplied to an HDD unit by either a 12 V_DC or a 5 V_DC power supply. However, as explained above, there is a tendency toward increases in the power consumption of HDD units, and so there is the possibility that it will no longer be possible to supply adequate power to HDD units using existing power supply terminals.
(2) The trends in recent years toward increases in the number of installed HDD units and toward increasing HDD internal power consumption have given rise to the need for larger-capacity power supply circuits for storage systems.
(3) In addition to existing HDD units requiring supply of a plurality of voltage levels such as 5 V_DC and 12 V_DC, HDD units which require the supply of other voltage levels are appearing. Consequently it is desirable that a single storage system be able to accept installation of a plurality of types of HDD units with different power supply specifications.
(4) There exist a plurality of various specifications for the interface for HDD unit data transfer, such as for example FC and SATA. Hence it is desirable that a single system be able to accept installation of a plurality of types of HDD units with different interface specifications.